This invention relates to novel multiple gas discharge display/memory panels or units which have an electrical memory and which are capable of producing a visual display or representation of data such as numerals, letters, television display, radar displays, binary words, etc.
Multiple gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characterized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being transversely oriented to define a plurality of discrete gas discharge units or cells.
In some prior art panels the discharge units are additionally defined by surrounding or confining physical structure such as by cells or apertures in perforated glass plates and the like so as to be physically isolated relative to other units. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the elemental gas volume of a selected discharge unit, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.
Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the A.C. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.
An example of a panel structure containing non-physically isolated or open discharge units is disclosed in U.S. Letters Patent 3,499,167 issued to Theodore C. Baker, et al.
An example of a panel containing physically isolated units is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled "The Plasma Display Panel-- A Digitally Addressable Display With Inherent Memory", Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, California, Nov. 1966, pages 541-547. Also reference is made to U.S. Letters Patent 3,559,190.
In the construction of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge units will be the product H .times. C and the number of elemental or discrete areas will be twice the number of such elemental discharge units.
In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing electrodes, but between two contiguous or adjacent electrodes on the same substrate; the gas being confined between the substrate and an outer retaining wall.
It is also feasible to have a gas discharge device wherein some of the conductive or electrode members are in direct contact with the gaseous medium and the remaining electrode members are appropriately insulated from such gas.
In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as shown herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly, i.e., a segmented display.
The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and a copious supply of charges (ions and electrons) during discharge. In an open cell Baker, et al. type panel, the gas pressure and the electric field are sufficient to laterally confine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing non-isolated units.
In prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in a gas discharge device. Typical of such gases include CO; CO.sub.2 ; halogens, nitrogen; NH.sub.3 ; oxygen; water vapor; hydrogen; hydrocarbons; P.sub.2 O.sub.5 ; boron fluoride; acid fumes; TiCl.sub.4 ; Group VIII gases; air; H.sub.2 O.sub.2 ; vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide; laughing gas; H.sub.2 S; deoxygenated air; phosphorus vapors; C.sub.2 H.sub.2 ; CH.sub.4 ; naphthalene vapor; anthracene; freon; ethyl alcohol; methylene bromide; heavy hydrogen; electron attaching gases; sulfur hexafluoride; tritium; radioactive gases; and the rare or inert gases.
In one preferred embodiment there is used a gas mixture comprising at least one rare gas, more preferably at least two, selected from neon, argon, xenon, and krypton. Beneficial amounts of mercury and/or helium may be present.
As described in the Baker, et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition at least one elemental volume other than the elemental volume in which the photons originated.
With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.
While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called "electrodeless discharge", such prior art devices utilized frequencies and spacings or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker, et al. invention.
The term "memory margin" is defined herein as ##EQU1## where V.sub.f is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not bi-stable and V.sub.E is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.
It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term "sustain a discharge" means producing a sequence of momentary discharges, one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.
In accordance with the practice of this invention, there is incorporated into the dielectric of a gas discharge device a beneficial amount of a source of at least one element selected from boron, gallium, indium, or thallium.
As used herein, the phrase "incorporated into" is intended to comprise any suitable means whereby a source of the selected element is appropriately combined with the dielectric, such as by intimately adding or mixing the source into the dielectric pre-melt batch or to the melt; by ion exchange; by ion implantation; by diffusion techniques; or by applying one or more layers to the charge storage surface of the dielectric, or to the electrode contact surface of the dielectric, or as an internal layer within the dielectric.
In one particular embodiment hereof, the source of the selected element is applied as one or more layers to the chargestorage surface of the dielectric.
As used herein, the term "layer" is intended to be all inclusive of other similar terms such as film, deposit, coating, finish, spread, covering, etc.
It is contemplated in such embodiment that the element source may be applied as a layer over previously applied dielectric layers. Likewise, layers of other substances may be applied over the layer of the element source. Such other dielectric layers may comprise phosphors and/or any other suitable compounds, especially inorganic oxides of Pb, Si, Al, Ti, Zr, Hf, Group IA, Group II, and the rare earths.
The source of B, Ga, In, or Tl, is applied to the dielectric surface (or over a previously applied layer) by any convenient means including not by way of limitation vapor deposition; vacuum deposition; chemical vapor deposition; wet spraying upon the surface a mixture or solution of the layer substance suspended or dissolved in a liquid followed by evaporation of the liquid; dry spraying of the layer upon the surface; thermal evaporation using direct heat, electron beam, or laser; plasma flame and/or arc spraying and/or deposition; and sputtering target techniques.
In a further embodiment hereof, a layer of an oxide of B, Ga, In, or Tl is applied to the dielectric surface, such as by one of the foregoing methods, especially electron beam evaporation.
In still a further embodiment of this invention, the oxide layer is formed in situ on the charge storage surface of the dielectric, such as by applying the element to the surface followed by oxidation.
Each layer of the source of B, Ga, In, or Tl is applied to the dielectric, as a surface or sub-layer, in an amount sufficient to obtain the desired beneficial result, usually to a thickness of at least about 100 angstrom units with a range of about 200 angstrom units per layer up to about 1 micron (10,000 angstrom units) per layer.
In the fabrication of a gaseous discharge panel, the dielectric material is typically applied to and cured on the surface of a supporting glass substrate or base to which the electrode or conductor elements have been previously applied. The glass substrate may be of any suitable composition such as a soda lime glass composition. Two glass substrates containing electrodes and cured dielectric are then appropriately sealed together, e.g., using thermal means, so as to form a panel.
In one preferred practice of this invention, each element containing layer is applied to the surface of the cured dielectric before the panel heat sealing cycle, with the substrate temperature during material application ranging from about 150.degree. F. to about 600.degree. F.
In the practice of this invention it is contemplated using any suitable source of boron, gallium, indium and/or thallium, especially inorganic compounds and more especially, inorganic oxides.
Although insulating or semi-conductor materials are typically used, conductor materials may be used if the material is appropriately isolated within or on the dielectric so as not to be in electrical contact with a source of potential and/or group. Likewise, if a conductive material is used in a multiple cell device, the geometric arrangement of the material may be such that no two cells are electrically connected by the conductive material. For example, the material could be deposited as a spot over each discharge site.
Typical inorganic compounds of boron include boron arsenate, boron tribromide, boron dibromide, boron monobromide, boron monopentahydride bromide, boron tetracarbide, boron trichloride, boron chloride, boron hydride (including B.sub.5 H.sub.11, B.sub.5 H.sub.9, B.sub.6 H.sub.10, B.sub.10 H.sub.14), boron triiodide, boron diiodide, boron monoiodide, boron nitride, boron oxide, boron phosphide, boron triselenide, boron hexasilicide, boron trisilicide, boron trisulfide, boron pentasulfide, and boron trichloride.
Typical compounds of gallium include gallium arsenide, gallium tribromide, gallium tribromide hexammine, gallium tribromide monammine, gallium perchlorate, gallium dichloride, gallium trichloride, gallium trichloride hexammine, gallium trichloride monoammine, gallium dibromide, gallium trichloride, gallium ferrocyanide, gallium trifluoride, gallium trifluoride triammine, gallium hydride, gallium triiodide, gallium triiodide hexammine, gallium triiodide monoammine, gallium nitrate, gallium nitride, gallium oxide (sesqui-beta or alpha), gallium suboxide, gallium oxychloride, gallium selenate, gallium monoselenide, gallium sesquiselenide, gallium subselenide, gallium sulfate, gallium monosulfide, gallium sesquisulfide, gallium subsulfide, gallium monotelluride, and gallium sesquitelluride.
Typical compounds of indium include indium antimonide, indium arsenide, indium dibromide, indium monobromide, indium tribromide, indium perchlorate, indium dichloride, indium monochloride, indium trichloride, indium cyanide, indium fluoride, indium iodate, indium diiodide, indium triiodide, indium monoiodide, indium nitrate, indium monoxide, indium sesquioxide, indium suboxide, indium phosphide, indium selenate, indium sesquiselenide, indium sulfate, indium monosulfide, indium sesquisulfide, indium subsulfide, indium basic sulfite, indium sesquitelluride, and indium telluride.
Typical compounds of thallium include thallium azide, thallium bromate, thallium dibromide, thallium monobromide, thallium tribromide, thallium dichloride, thallium monochloride, thallium trichloride, thallium carbonate, thallium chlorate, thallium perchlorate, thallium chloroplatinate, thallium chromate, thallium dichromate, thallium chrominum sulfate, thallium cyanate, thallium cyanide, thallium ferrocyanide, thallium fluogallate, thallium monofluoride, thallium trifluoride, thallium fluosilicate, thallium iodate, thallium iodide (alpha and beta), thallium triiodide, thallium magnesium sulfate, thallium molybdate, thallium nitrate (alpha, beta, and gamma), thallium nitrate, thallium nitrite, thallium oxide (Tl.sub.2 O, Tl.sub.2 O.sub.3), thallium orthophosphate, thallium di-beta-orthophosphate, thallium pyrophosphate, thallium rhodanide, thallium selenate, thallium selenide, thallium silver nitrate, thallium sulfate, thallium sulfate hydrogen, thallium sulfide, thallium sulfite, thallium metatellurate, thallium thiocyanate, thallium dithionate, thallium thiosulfate, thallium metavanadate, and thallium pyrovanadate.
The use of a source of B, Ga, In, and/or Tl, in accordance with this invention has many potential benefits. For example, sources of such elements may be utilized alone, or in combination with other elements (as noted hereinbefore), to achieve lower panel operating voltages, thermal stability, more uniform panel operating voltages, decreased aging cycle time, etc.
The source of B, Ga, In, and/or Tl used in this invention may be of any suitable state, preferably as a solid. However, a liquid or gaseous state may be utilized, e.g., combined with a suitable binder.